The present invention relates to a metering method of an injection molding machine and, more particularly, to a metering method for an injection molding machine which uses a servo motor to drive a screw in a direction of a screw shaft, to perform injection, and to supply a back pressure.
In a conventional injection molding machine, hydraulic pressure is used as a source to drive a screw in an axial direction. In this conventional case, during metering, a predetermined pressure is supplied by a hydraulic pressure to the screw in the axial direction, with the screw being rotated. As the resin is melted, the molten resin is stocked in the distal end portion of the screw and the screw is then moved backward. When the screw backward movement position reaches a metering point, the rotation of the screw and application of the back pressure to the screw are stopped. However, even if rotation of the screw and application of the back pressure are stopped when the metering is completed, the screw is moved backward by the molten pressure of the resin and so on, resulting in a metering error. When the metering is incorrect and the injection amount is large, a burr may occur in a molded product. When the injection amount is insufficient, the resin cannot easily flow in a thin portion. As a result, a high-quality molded product cannot be obtained.